This is an interdisciplinary research project between the departments of Neuroradiology and Neurology at Columbia University. It is proposed to study the neurotoxic effect an angiographic water soluble contrast media on electrically evoked neural activity in the central nervous system. It is hoped that through the utilization of this basic model, a new water soluble radiopaque substance will be developed for the safe intrathecal administration and the examination of the cerebral cortex. The pilot study conducted by the investigators in 17 cats, indicates that a safe pharmacological antagonist can be developed. A few candidate substances are currently under investigation and will be further studied during this project. It must be noted that even the recently introduced water soluble myelographic agent, Metrizamide, has so much neurotoxicity as to preclude its use above the cervical spine.